1. Field of the Invention
The present invention relates to a piston assembly for compressors, and more particularly to a piston assembly of the so-called ball joint type which is useful for compressors and in which a piston is connected to a crankshaft by a connecting rod having a ball at its one end, with the ball held in contact with a ball seat formed in the piston.
2. Description of the Prior Art
As disclosed, for example, in examined Japanese patent publication No. 45(1970)-40204, conventional piston assemblies of this type for use in compressors include, as shown in FIG. 6, a connecting rod 33 connecting a piston 32 to the crankpin 31 of a crankshaft 30 and having a ball 34 at its one end. The ball 34 is in contact with a ball seat 35 formed in the piston 32, while the piston 32 is formed at its rear end with a hollow cylindrical clamp portion 36 which is clamped toward the ball 34 to hold the ball 34 joined to the piston 32. The crankpin 31 has an oil outlet 37 for scattering an oil toward the piston upon ejection therefrom to cause the oil to fall onto the clamp portion 36 and thereby lubricate the surface of the ball 34 in sliding contact with the clamp portion 36.
With the above construction, the sliding surface of the piston 32 and the sliding surface of the ball 34 positioned toward the crankpin 31 are almost entirely covered with the clamp portion 36, and the clamp portion 36 is entirely covered with the skirt portion 38 of the piston 32, so that the oil forced out from the oil outlet 37 of the crankpin 31 is acutally applied to the sliding surfaces of the piston 31 and the ball 34 only in a very small amount. Thus, there arises the problem that these surfaces are prone to improper lubrication. This problem impairs the free movement of the piston assembly of the ball joint type to permit uneven contact or wear of the piston, causing the compressor to consume an increased amount of power and lowering the reliability thereof.
The main object of the present invention, which has been accomplished in view of the above problems, is to provide a piston assembly of the type described for compressors wherein the piston and the ball are given improved lubrication characteristics at their sliding surfaces to preclude uneven contact or wear of the piston and thereby reduce the power consumption of the compressor and improve the reliability thereof.